The reproductive biology and spawning strategy of the iconic catadromous percichthyid, estuary perch Macquaria colonorum was examined from three coastal rivers of south-eastern (SE) Australia. Ovarian and testicular development followed a pattern similar to that of other percichthyids, world-wide. Females were collected in significantly larger sizes and greater numbers from all, and two of the three rivers, respectively. Mean size and age at maturity was greater for females (25.05 cm FL±0.85 and 3.75 yrs±0.08, respectively) than males (22.21 cm FL±0.50 and 3.28 yrs±0.08 respectively), with no significant difference between rivers. Trends in gonadosomatic indices indicated that M. colonorum spawn in the austral winter-spring in SE Australia. However, peak spawning occurred earlier (June-August) in the two most northern rivers (Hawkesbury and Clyde) compared with the Bemm River (September-November) further south. Ripe females were captured only in the lower reaches of estuaries throughout the spawning period in all three rivers. Mature M. colonorum females displayed a group synchronous pattern of oocyte development suggesting a multiple spawning strategy. Mean batch fecundity (F B ) was 266 583±17 821 oocytes per female and relative fecundity was 377±10 oocytes.g -1 body weight. There were significant power relationships between F B and fork length (FL), weight and age. Similar to other percichthyids, M. colonorum are longlived, highly fecund and exhibit a flexible spawning strategy which is attuned to the highly variable environments in which they are found.

Temperate basses and perches (family Percichthyidae) worldwide have declined in distribution and abundance during the past few decades due to anthropogenic impacts such as fishing, habitat degradation and alteration to river flows. This study examined differences in the age, growth and longevity of Macquaria colonorum among three south-eastern Australian coastal rivers. Estimates of ages were made by counting opaque zones in sectioned otoliths. Ages were validated by using marginal increment analysis, staining fish otoliths with oxytetracycline and sampling young-of-the-year fish. Length-at-age data from 1644 fish indicated that growth of M. colonorum is rapid in the first 3 to 4 years, after which it slows considerably. Females grew faster and reached larger asymptotic lengths than males. The species was found to be long lived, with the oldest fish estimated at 41 years. Population age structures indicated variable year-class strengths in all three rivers and there was an absence of larger, older (>10 years) individuals in the populations from the two rivers with a history of commercial fishing. These results indicate that M. colonorum populations, similar to other global percichthyid and estuarine-dependent fishes, have been subjected to episodic recruitment and age truncation and that these are likely influenced by environmental flows and fishing pressure.

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The electrochemical measurement of the corrosion rate of zinc in nearneutral solutions using a differential pulse polarograph has been achieved to a greatly improved accuracy compared with previous w~rk. The perturbation of the corroding system is minimized as the potentiostatic polarizing pulse is applied for only 60 msec. The double layer charging of the electrode is monitored on an oscilloscope and the faradaic current measurements made by the normal Y recorder output of the polarograph. The iR correction facility on the polarograph is used to determine the Tafel parameters and can also be used if resistance overvoltage is a problem during the polarization resistance measurements. Four different solutions are examined where the cathodic processes are either separately or jointly oxygen reduction or hydrogen evolution. Where only one cathodic process occurs, the correlation of the weight loss with the corrosion current calculated by the Stern-Geary method is within 7%. Where two cathodic processes occur, errors of up to 15% are encountered.Recent studies on the corrosion of zinc in aerated near-neutral aqueous solutions (1-3) highlight two important areas which have been overlooked in past investigations. The first is a comprehensive study of the cathodic reactions which control the rate of corrosion of zinc in these solutions. Despite the common use of zinc as a sacrificial coating, a thorough study of the oxygen reduction reaction on zinc has been reported only recently (1) and it is obvious from this work that a concurrent hydrogen evolution reaction occurs in near-neutral solutions. Therefore, the exact nature of the cathodic reactions on zinc still requires further investigation to determine the extent of the hydrogen evolution in near-neutral solutions.The second area where further research is required is in the electrochemical methods for determining instantaneous corrosion rates. When studying corrosion reactions and particularly at rotating ring-disk electrodes, it is important to be able to monitor the corrosion rate of the disk because the cathodic reactions are usually surface dependent and, therefore, vary throughout the course of any one experiment. The refinement of simple methods such as linear polarization (4, 5) by Oldham and Mansfeld (6, 7) and the derivation of new methods by Barnartt (8) and others (9-11) have not produced any dramatic improvements in the correlations between electrochemically calculated corrosion currents and the weight loss for zinc freely corroding in aqueous solution. Impedance measurements (12) have been shown to yield reasonably accurate corrosion rates for steel, but they are limited to reactions where the corrosion current does not alter during the course of the experiments. In practice, this does not usually occur, particularly where corrosion products are formed on the surface.It has been our experience with corrosion rate measurements that the inaccuracies in determining the polarization resistance, AE/Ai, and Tafel parameters usually result in far greater errors...